Try torx....Some torx screws bhave a pin in the middle preventing the use of torx bits that don't have a hole in the center. These are the tamper-proof type found on hard drives and telephone equipment.Hope this helps a little....

Hard to see in that picture. Torx is a six pointed star, whereas Allen is a plain hexagon. Should be easy enough to distinguish in the flesh, and if its Allen then I would expect it to be metric sized.